Pathophysiology of Hyperkalemia

1) hyperkalemia is plasma K+ > 5.0 mmol/L (if > 7.5 mmol/L, becomes life threatening
2) caused by increased release from cells (intravascular hemolysis, tumor lysis syndrome, rhabdomyolysis), decreased clearance by kidney due to acute or chronic kidney failure, excess intake (often iatrogenic)

Signs and Symptoms

1) weakness up to flaccid paralysis
2) cardiac excitablity

Characteristic Test Findings

EKG

1) peaked T waves are characteristic of hyperkalemia
2) prolonged PR interval
3) widening of QRS
4) absent P waves
5) ventricular arrhythmias (ventricular tachycardia, ventricular fibrillation)

Associated Conditions

1) metabolic acidosis (due to intracellular buffering of H+)
2) hyperglycemia
3) digitalis toxicity
4) hemolysis
5) hyperaldosteronism (Conn’s disease)
6) Addison’s disease
7) K+ sparing diuretics (spironolactone)
8) ACE inhibitors
9) NSAIDs
10) cyclosporine
11) trimethoprim
12) pentamidine

Biochemistry

hyperkalemia partially depolarizes cardiac cell membranes

Treatment

1) aim is to shift K+ into cells and promote K+ loss
2) 25-50 g of Kayexalate (sodium polystyrene sulfonate) with 100 mL of 20% sorbitol by mouth or enema (cation exchange agent)
3) 1 ampute of calcium gluconate (decreases membrane excitability), 50 g IV glucose, and 10-20 units of regular insuline IV (causes K+ to shift into cells)
4) beta2-adrenergic agonists via IV of nebulizer (effect lasts 2-4 h)
5) extremed hyperkalemia is treated with dialysis with low K+ dialysate
6) alkali therapy with 3 ampules of NaHCO3 per liter IV

Tips for USMLE

if question mentions peaked T waves on EKG, think hyperkalemia or anterior cardiac ischemia